Cardiac rhythm or function management devices can include implantable devices to help maintain heart rhythm or function. Cardiac rhythm or function management devices can include pacers, defibrillators, cardioverters, cardiac resynchronization therapy (CRT), or various combinations of these or other devices. In various examples, cardiac rhythm or function management devices can sense intrinsic heart contractions, deliver pacing pulses to evoke responsive heart contractions, or deliver a shock to interrupt certain arrhythmias. In certain examples, one or more of these functions can help improve a patient's heart rhythm or can help coordinate a spatial nature of a heart contraction, either of which can improve cardiac output of blood to help meet the patient's metabolic need for such cardiac output.